Halothane-induced hepatotoxicity, which is often fatal in humans, is believed to have an immunological basis, since this disease is nearly always associated with repeated administration of halothane. The most likely metabolite of halothane to become haptenic is trifluoroacetyl chloride, which can bind to tissue protein and phospholipid. In this regard we have raised antibodies directed against the trifluoroacetyl group by immunizing rabbit with trifluoroacetylated rabbit serum albumin. We intend to use these antibodies to determine whether patients or animals receiving halothane have trifluoroacetyl groups bound to their hepatocytes. We intend to determine whether these altered hepatocyte membranes can initiate an immune response, which can result in hepatocellular damage. These immunological studies with halothane may serve as a model for the toxicity of other compounds which are believed to have an immunological origin.